Refining hydrocarbon oils



March 12, 1946. G. H. CUMMINGS ET AL 2,396,303

REFINING HYDROCARBON OILS Filed Deo. 7, 1940 5 Sheets-Sheet l AAA ....A A AAA AvAyAyAvAvAvAxAzAyAVAVA AvAvAvAvAYAYAVAvAzAyAvAvA vvv vw' vvAv March l2, 1946. G, H CUMWNGS ETAL 2,396,303

REFINING HYDROCARBON OILS Filed Deo. 7, 1940 5 Sheets-Sheet 2 OO 80 .SLveNT G. H. cuMMlNGs ET AL 2,396,303

REFINING HYDROCARBON OILS 5 Sheets-Sheet 3 Filed Deo. '7, 1940 March 12, 1946.

`March 12, 1946.

G. H. cuMMvlNGs ETA| REFINING HYDROCARBON OILS Filed Dec. '7, 1940 5 Sheets-Sheet 4 Patented Mar. 12, 1946 REFINING HYDROCARBON OILS George H. Cummings, State College, Pa., William J. Sweeney, Elizabeth, N. J., and Merrell R. Fenske, State College, Pa., assignors of onehalf to Standard Oil Development Company, a corporation of Delaware, and one-half to Rhm & Haas Company, a corporation ol Delaware Application December 7, 1940, Serial No. 369,055

19 Claims.

The present invention relates to the refining of mineral oils and is particularly concerned with the separation and recovery of aromatics from feed mixtures containing the same. In accordance with the present process, mineral oils or treated fractions thereof, such as would be obtained in the processing of petroleum fractions or in the coking of soft coals, are treated in a manner to segregate the aromatics, utilizing a particularly desirable solvent which comprises ammonia and a substance having the ability to control the solvent power of the ammonia within critical limits. This application contains subject matter in common with and is a continuation-in-part of our application Serial No. 353,448, filed August 21, 1940.

The major source of the lower boiling aromatics such as benzene, toluene, and the xylenes,

However, the supply of these is from coal tar. materials can be increased. It has been demonstrated that by cracking various petroleum products, or by the catalytic dehydrogenation or cyclization of certain petroleum fractions, aromatic hydrocarbons can be produced. Furthermore, in cert-ain mineral oils aromatic hydrocarbons occur in reasonable concentrations. There is then a great need for a process that (a) will permit these aromatics to be separated in a high degree of purity from the other hydrocarbons with which they are associated, and (b) also permit their recovery in high yields. In general, only by fairly complete recovery of aromatic constituents in a high purity can these newer processes compete with those utilizing coal tar as their raw material. grated process is available for recovering aromatics in high yields and in high purities from mineral oils. Distillation is not always a possible method due to the overlapping of boiling points of various hydrocarbons withthose of the aromatic hydrocarbons. In general, distillation is not a successful means for obtaining pure aromatics in high yields from mineral oils. Although organic solvents, such as phenol, furfural, cresols, nitrobenzenes, aniline, beta beta dichlorodiethyl ether and the like, have been in use for some time for segregating the more aromatic from the more paraflinic constituents of lubricating oils so as to prepare improved oils, these solvents are generally unsatisfactory for separations in the lower molecular weight range, that is, in the range below lubricating oils. When these solvents are used on hydrocarbons of the character of lubricating oils there is still great diiculty in preparing pure aromatic extracts, and as a Up to the present no unified and inte-.

generaI rule. pure aromatic extracts are not obtainable. This is due (a) to pure aromatics being completely soluble in the solvents now in use,

. partially miscible with the solvent. Despite the development of processes and procedures for utilizing solvents for refining and separating petroleum hydrocarbons, there is still no unified' 'solvent-treating operation wherein pure aromatics are completely recoverable. Nor does it follow that a mere extension or intensification of such processes and procedures will aord the desired result since, as indicated, a principal dimculty lies in the solvent, and its inability to operate in a practical manner at various points in the extraction operation with the proper value of selectivity and solvent power. Heretofore, in cases where the purity of aromatics may be high their degree of recovery from the raftinate is limited; conversely, when their recovery is high (i. e., 'the raninates are aromatic-free) their purity is definitely restricted. One feature of the present invention is the simultaneous preparation of pure aromatics and their recovery' in high yields from the raiiinate.

With the exception of the Edeleanu process solvent extraction has not been widely applied to separations in the lower molecular weight range. Even inthis process, the object usually is not the production of pure aromatics, but rather the dearomatizing of a petroleum fraction with the result that the extract is contaminated with a considerable proportion of non-aromatics. Indeed, sulfur dioxide is not readily applicable to the production of pure aromatics due to its very great solvent power for these compounds. Various other solvents have been proposed for the segregation of certain specic lower molecular weight compounds, and particularly aromatics, but all of those solvents have been subject to certain limitations which have prevented their commercial use. A primary limitation has been the inability of solvents to possess a proper range of solvent power and still have good selectivity. This isnot unusual for it is common knowledge that pure aromatics are exceptionally good solvents for organic compounds. Consequently, itis diicult if not impossible for most solvents to yield relatively pure aromatics by extracting mineral oils. The solvent plus the aromatics is such a potent solvent combination that considerable proportions of non-aromatic constituents are naturally dissolved along with the aromatics, and so contaminate them. If the solvent power of the solvent is lowered so as to reduce the proportion of non-aromatic constituents incorporated in an extract, then such a solventl usually possesses too low a solvent power for the feed stock, for the concentration of aromatics in mineral oil fractions is frequently of the order of 30 per cent or less. A low solvent power for the feed means excessive solvent-to-oil ratios if a high recovery of aromatics from the feed is to be insured. The solution to this dilemma of a solvent possessing too low a solvent power on one hand, and too great a solvent power on the other has heretofore not been propounded.

Our invention has been the discovery of a practical solvent system, based on liquid ammonia, which is applicable to the separation of aromatics from mineral oils in any desired degree of purity and in any desired yield over a wide molecular weight range.

One method for studying the type of separations possible with a given solvent is to prepare binary mixtures of representative members of the two types of constituents being considered, and determine equilibrium relationships between the binary mixtures and the solvent. These equilibrium data can then be plotted on triangular graphs, from which calculations of the solvent-to-oil ratio and number of theoretical stages necessary for a given separation can be made. (The properties of triangular graphs are covered thoroughly by Roozeboom, Die Heterogenen Gleichgewichte.v They are summarized by Hunter and Nash, J. Soc. Chem. Ind. 53, 95T (1934) The latter article and one by Varteressian and Fenske, Ind. Eng. Chem. 29, 270 (1937) summarize methods of calculations.) In the triangular graphs each apex of the triangle represents a component oi' the mixture which components are the solvent and the two hydrocarbons involved. A perpendicular from each apex to the opposite side is divided into 100 equal parts. Lines which pass through these points, parallel to the opposite side, represent lines of constant percentage of the particular component represented by the opposite vertex. Any liquid mixture of three components can be represented by a point on the graph. The perpendicular distance from this point to any side is proportional to the percentage of the component represented by the opposite vertex. If two liquid solutions are mixed, the compositions of the resultant solution will be represented by a point on a straight line between the composition points of the two original solutions, and the proportion of each original solution will be inversely proportional to the distance between its composition point and the final composition point. For example, in the equilibrium diagrams of Figures 1 and 2 the area under the binodal curve (Figure l) or between the two solubility lines (Figure 2) represents a two-phase area. A solution whose composition falls within this area, under the conditions of pressure and temperature represented by this diagram, will break up into two liquid phases of definite composition. The composition oi.' these eouilibrlum phases will be represented by an equilibrium or tie-line drawn through the original overall composition point and terminating at the two solubility lines. The shape of the curve and the position of the tie-lines are determined experimentally. It is evident that for any enrichment, or separation of the hydrocarbon mixture to occur, two phases must be formed. Thus, in Figure 2 either component could be made pure, but in Figure 1 a maximum purity of 73 per cent A under the conditions of the diagram would be reached, since above this value only one phase appears and no further enriching could occur.

Certain features of our invention can be understood with the help of Figures 1 and 2. For example, many organic solvents as well as sulfur dioxide exhibit diagrams similar to Figure l. That is, the solvent is completely miscible with the more soluble component A, with the limitations on the purity of A as already noted. A mixture of 20 per cent aromatics and 80 per cent non-aromatica may be represented as a mixture of 20 per cent A on Figure l. If one part of this mixture is treated with 3 parts of solvent, the solubility at the feed is shown by point F, namely, about 8 per cent. Yet, if this solvent layer is passed to an enriching section to increase the concentration of A dissolved therein, the maximum purity of A is '73 per cent, and the solubility is represented by point E, which is a value of 40 per cent. This value is altogether too high. It naturally means that complete miscibility is near. It is typical of this condition of complete miscibility of solvent and aromatics. Further, the selectivity as judged from the top tie-line will be found to be low for when complete miscibility is reached there is no selectivity. At the raffinate end of the extraction zone the solubility is very low, about 4 per cent as represented by 85 point R. As indicated, this diagram typiiles many solvents. Aromatic-free raiiinates are possible, but pure aromatics do not result. Also, the solubility varies widely throughout the extraction zone, being about 4 per cent at the rainate end 40 and 40 per cent at the extract end. The type of diagram resulting from a pursuance of our invention is typified by Figure 2. Here pure aromatics can be obtained since the solvent is incompletely miscible therewith. Also, their recovery in high yields is possible by virtue of the desirable solubility prevailing at the feed point. Using the previous example, a mixture of 20 per cent aromatics when now treated with 3 parts of solvent exhibits a feed solubility of 14 per cent, shown by point F'. Partial miscibility exists at all points in the enriching section, the solubility at the extract end increasing to 18 per cent, as represented by E. Further, the solubility at the rafllnate end is shown by point R' to be about l2 per cent. Thus high recovery yields of aromatics are insured. 4Figure 2 shows clearly the fact that the solubility has been controlled at three vital points in a solvent-treating operation, namely, at the extract end, at the feed point, and at the rainate end.

When ammonia is modified according to our invention, the equilibrium and solubility relationships may be characterized by Figure 2. Both components of the feed mixture may be made as pure as desired. This is one advantage of our invention. Other advantages will be apparent from the further disclosures.

In order to secure a clear concept and value of a particular solvent a selectivity factor, termed beta, is employed. This factor is quite analogous to the alpha factor employed in distillation and may be represented by the following formula:

in which the terms X and Y are used to denote concentrations in the raiiinate and extract or solvent phases, respectively, while A and B denote, respectively. the more soluble and less soluof the more soluble component to the less solublel component in the solvent or extract phase, and XA/XB equals the ratio of the more soluble component to the less soluble component in the oil 'or raffinate phase. Beta is a numerical measure of the solvents selectivity or the solvents ability to dissolve preferentially one particular type of constituent to the exclusion of other types of constituents.

'I'he beta or selectivity of any particular organic solvent may be affected by the ,addition of other materials to the solvent. Generally, as the solvent power of any solvent is altered the selectivity or beta decreases to a marked extent. This is particularly the case when employing liquid sulfur dioxide which is of a character similar to the character of liquid ammonia. Liquid sulfur dioxide, even with the use of modifying solvents, is subject to other limitations in the purity of' extract obtainable, even at very low temperatures. Organic solvents which have been found satisfactory for lubricating oil extraction and high molecular weight separations, such as phenol, chlorex, furfural, cresylic acid, etc., are unsuitable for the treatment of lighter hydrocarbons, i. e., hydrocarbon fractions boiling below a typical light lubricating oil, Various substances have been added to the foregoing and other solvents to obtain more or less improved operation in treating oils and particularly relatively high molecular Weight hydrocarbons. In many cases such other substances are added to alter density relationships. thereby facilitating phase separation. They are also added to reduce emulsions, Their effect on the solvent power or selectivity of the particular solvent to which they are added is obscure since the function and choice of such materials depend on their ability to disengage the` solvent and oil phases more rapidly than would otherwise be possible. The selection of such substances also depends on the properties of the solvent and the oil being treated.

In some cases other liquids have` been added to a particular solvent in order to alter its solvent power. The effectiveness of these added liquids depends largely on the properties and characteristics of the primary solvent to which they are added. For most of the primary solvents in present use vary few modifying solvents may be extensively used due to difculties experienced with density factors, emulsions, mutual solubility, chemical interaction, corrosion, etc. Some of the combinations in use are accompanied by unforeseen difficulties. lior example. when benzol is added to liquid sulfur dioxide to adjust the solvent power of the solvent. the selectivity as measured by beta drops considerably and to an almost prohibitive extent. Adding water to phenol reduces its solvent power for oil, but the` phenolwater mixtures are considerably more corrosive than either phenol or water alone. In some cases there are also emulsion troubles. Very few liquids may be added to furfural or chlorex due to their relatively great vchemical reactivity, It is well known that few. if any, liquids soluble in liquid sulfur dioxide will reduce its solvent power without chemical reaction or causing the corrosion of equipment, No wholly satisfactory solvent has yet been found for changing the dissolving power of liquid sulfur dioxide Without impairment of its selectivity due to the properties of sulfur dioxide. In general, experience has shown that'there are several disadvantages to the use of modifying solvents as heretofore employed. These disadvantages include: loss of selectivity, increase in corrosivencss, the production of emulsions, diniculty in separating the modifying solvent from the primary solvent, difculty in separating the primary solvent or `modifying solvent from the be made.

hydrocarbon mixture being treated. and incompatibility of the modifying solvent with the primary solvent over a relatively wide range of concentration or hydrocarbon solubility. This is a particular obstacle if more than two products are to be obtainedfrom any one solvent-treating operation. However, a principal disadvantage of employing a modifying solvent to alter the solvent power of a particular solvent is that a loss in the selectivity of the solvent occurs as measured by a lower beta.

Although liquid ammonia is exceptionally well suited as a basis for a solvent system for the segregation of pure aromatics in the boiling range below lubricating oils, liquid anhydrous ammonia alone is not particularly well adapted to other than a few specific separations. In many cases itis inapplicable to aromatic separations. For example, the miscibility temperature of benzene and liquid anhydrous ammonia is so low that benzene will not separate as a liquid phase, but rather precipitates 'as a solid. Hence pure benzene cannot be separated from hydrocarbon mixn tures by this solvent. A similar condition exists with naphthalene. The miscibility temperature for equal volumes of liquid anhydrous ammonia and toluene is 19 F. Even at zero degree Fahrenheit the solubility of toluene in ammonia is so high that the selectivity or beta is reduced to a value where economical separations cannot On the other hand, n-octane, which has a boiling point very close to toluene and from which toluene must often be separated, is soluble only to the extent of six per cent in ammonia at F. In the separation of n-octane-toluene mixtures, in the stripping zone of the tower the solubility in the solvent must be high enough to remove substantially all the toluene at economically low solvent-to-oil ratios in orderto obtain a good yield of toluene. whereas in the enriching zone toluene must not only be incompletely miscible with the ammonia but also have a low enough solubility so that the selectivity or beta is high and pure toluene is obtainable. These conditions are such that liquid anhydrous ammonia cannot be used for the economical purification of toluene. Similar conditions exist for many other members of the aromatic series.

Furthermore from the prior art it is not to be expected that these inherent disadvantages nossessed by liquid anhydrous ammonia could be nectied by methods as known tothe art. For example, modifying substances employed in conjunction with organic solvents materially affect the selectivity or beta of the solvent. This effect on the selectivity of the solvent seems to be increased when emploving a solvent selected from the class of liquefied normally gaseous inorganic solvents. For example, benzene when employed in conjunction with sulfur dioxide reduces the selectivity of the sulfur dioxide to a small fraction of its former value. This greatly impairs or prohibits the use of sulfur dioxide in many cases where it would otherwise be very applicable. In fact, no inorganic selective solvent has been proposed to which modifying solvents may be added without critically impairing the selectivity of the solvent.

We have, however, discovered that, providing the solvent comprises ammonia and a modifying agent, unexpected desirable results are secured. We have discovered that, providing the characteristics of ammonia be modified with the desired modifying agent, it is possible to treat feed oils for the production of products which otherwise could not be secured either by the use of ammonia alone or by means of closely related solvents. We have discovered that ammonia is compatible with a variety of substances capable of varying its solvent power for hydrocarbons, that when these modifying agents for adjusting solvent power over a definite range are used, little, if any, loss in selectivity occurs, and that there is substantially no increase in corrosiveness or in emulsions. Thus, in spite of the fact that no selective solvent in present use is susceptible to modifying agents for altering solvent power without some of the previously noted disadvantages occurring, we have discovered that ammonia is compatible with a great many substances without such disadvantages and, that by proper choice of modifying agents, the ammonia solvents may now be used to segregate pure aromatics in high yields over a wide molecular weight range.

Suitable modifying agents can be chosen from a relatively large group. Any substance which will not react but which when added to the system will alter the solvent power of the ammonia may be used. As specific examples we may cite water, ethylene glycol, formamide, ethylene diamine, some naphthenic hydrocarbons and paraiilnc hydrocarbons to reduce the solvent power, and higher glycols, ethers and ether-alcohols, methanol and other alcohols, alcohol-amines, aniline, pyridine, the methylamines and other low molecular weight aliphatic amines to raise vthe solvent power. We have found that water ethylene glycol, the methylamines, the lower molecular weight diamines, and parafflnic or naphthenic-type hydrocarbons are especially effective. We have found particularly that hydrocarbons which distribute themselves between the extract and railinate phases in such a way that they appear predominantly in the raiiinate phases are very efficient in lowering the solvent power ofthe liquid ammonia. It is to be understood that such hydrocarbons, to be added to reduce the solvent power of ammonia, will be selected so they can be separated from the hydrocarbons being extracted, usually by means of distillation. In extracting aromatics from feed mixtures boiling in the gasoline range, it is usually satisfactory to select parafilnic or naphthenic-type hydrocarbons having molecular weights of the order of 50 or more units higher than the highest molecular weight component being extracted. In treating kerosenes and non-viscous oils this same procedure is satisfactory. However, it is also a good procedure to select the 'parailinic or naphthenic hydrocarbons so that their highest molecular weight constituent is of the order oi 50 or more units lower in molecular Weight than the lowest molecular weight component of the mixture being extracted. In extracting viscous oils. the recommended procedure is to select relatively non-vis# cous lower molecular weight parafllnic or naphl thenic hydrocarbons. Hydrocarbons of the character of Nulol are satisfactory for treating gasoline and kerosene fractions. In fractions containing aromatics, such as benzene, toluene, and xylene, hydrocarbons such as decane, cetane, triand tetra-isobutane and decalin are satisfactory.

. Such hydrocarbons are also suitable when segregating aromatics from oils having molecular weights ranging from about 250 to about 500. In some cases, we find it advisable to add one type of modifying agent in one zone of the extraction and another type at another zone, the resulting solvent being composed of three components: ammonia; a. modifying agent for increasing the solvent; and one for decreasing it. In general, the solvent in the solvent phase will be composed predominantly of ammonia, i. e., above 50 per cent by volume, such that the selectivity characteristics of the solvent are primarily that of the ammonia; only the solvent power is modified. Hence, it is not necessary that the modifying agent be selective. It is only necessary that it alter the solvent power of the ammonia. Our modifying agents should not be confused with those substances added to ammonia to change its specific gravity in order to afford better phase separation. Such substances may not affect the solvent power; for example, inorganic salts may be added. For our modifying agents, on the other hand, the primary requisite is that they change the solubility of the hydrocarbon in the solvent, and they are chosen primarily on the direction and degree that they do this.

As just noted, it is not necessary that the modifying agent be completely soluble in the liquid ammonia, for paraiinic or naphthenic hydrocarbons may be added to lower the solubility in the ammonia solvent. In general, this type of modifying agent will proportion itself so that it appears in a greater concentration in the raiiinate than in the extract. We prefer that it occur in minor molecular proportions in the raffinate so that it acts as a modifying agent for the solvent power of ammonia, and not as a solvent itself. It, of course, need not necessarily be a hydrocarbon so long as it functions as indicated.

By the use of modifying agents of various types and in various amountslit is possible to obtain any degree of solvent power for any particular hydrocarbon component. However, we have found that it is preferable to confine this solubility to relatively definite limits, particularly at the feed point in a countercurrent extraction apparatus. We prefer that the conditions of extraction be so adjusted, that, at the hydrocarbon feed point, the solubility of the hydrocarbon in the solvent lie in the range from 5 to 30 per cent. We have further found that the selectivity, or beta, for ammonia together with a modifying solvent is closely dependent upon this hydrocarbon solubility in the solvent, for beta and the solubility control the number of stages required and the solvent-to-oil ratio needed. Figure 3, which is based on an aromatic-paraffin hydrocarbon mixture, shows, for a given separation. typical curves for the variation of minimum solventto-oil ratio and minimum stages with hydrocarbon solubility in the solvent. It clearly demonstrates that when the solubility is too high, both the solvent-to-oil ratio and the stages required are too high to be economically feasible. Likewise, for very low solubilities, a very high solvent-to-oil ratio is required. The position of these curves will be displaced for different specific mixtures and for different type compounds. and the minimum point for solvent-to-oil ratio will be shifted, but the general shape will remain the same. In general, the amount of modifying agents is controlled so that about to 30 per cent solubility is secured at the feed point. Desirable operation for the Case just illustrated comprises one in which the solubility is in the range of about 15 to 25 per cent, particularly in the range of about 20 to 22 per cent. However, this optimum solubility will vary depending upon the particular feed stock being treated and general operating conditions.

The' ammonia and the modifying agent may partition themselves between the extract and rafnate phases in a different concentration ratio. As a result, when countercurrent treating operations are being employed, the composition of the solvent may change along the countercurrent path. In general, this composition change will,

have a beneficial effect, for the solvent usually decreases in solvent power because of this change as it Hows through the countercurrent extraction path. This eiect aids in maintaining the solubility at a more constant value, and leads to more eiiicient extraction.

These modifying agents may be added directly to the ammonia, or they may be added to a countercurrent treating system at several points. We have found the addition of the modifying agent at one or more points in a countercurrent extraction path to be particularly eective. In this way the solubility is controlled so as always to be within the proper limits in order that the selectivity, or beta, may be high. It is frequently much more feasible and practical to control the solubility in this way than in other ways, for example, by changing the temperature.

In the segregation of pure aromatics by our ammonia solvents it is often desirable to employ two extraction zones: a stripping zone Where substantially all the aromatics are removed from the feed oil, and an enriching zonewhere the aromatics are puried from the other components which are of necessity dissolved with the aromatics in the stripping zone, but to a lesser degree. Due to the great differences in solubility between the aromatics and the other components, it is often preferable to employ different solvent power for the solvent in the two zones. This may be done either by temperature or by control of the modifying agent concentration,

or by use of different modifying agents. We have found that adjusting the modifying agent is the more economical method, and this is a preferred modification of our invention.

The amount of modifying agent added depends upon the degree to which the solvent power should be changed, and hence upon the mixture Abeing extracted and the particular modifying agent used. In general, the solvent mixture should comprise at least fifty per cent ammonia. When treating mono-cylic aromatics with less than twelve carbon atoms, or di-cylic aromatics with less than fteen carbon atoms we prefer that modifying agents he chosen so that the solvent has a lower dissolving capacity than liquid anhydrous ammonia at the extract end of the tower. This permits the extraction to be carried out at temperatures not differing greatly from normal. In these extractions we have frequently found it desirable to employ a dissolving capacity equal to or greater than liquid anhydrous ammonia at the raffinate end of the tower so that high yields of the aromatics may be obtained with reasonable and not excessive solvent-tooil ratios. In these cases the solvent may be composed of ammonia and a modifying agenty to raise the solvent power in the stripping zone. A modifying agent to reduce the solvent power will then be added at one or more points in the enriching zone. This enables the high yields of aromatics afforded by the proper solubility control in the stripping zone to be further processed in the enriching zone to produce aromatics of high purity.

These points will be clearer from the following examples which are given by way of illustration only and should not be construed as limiting the invention in any manner whatsoever.

Elample 1 A mixture consisting of 25 per cent benzene in cyclohexane was extracted at F. with an ammonia-water solvent. Five per cent water was in the ammonia at the raiiinate end of the tower, while water injection along the solvent path raised the water concentration to 20 per cent at the extract end. Using a solvent-to-oil ratio of four-to-one, and an extraction operation .similar to Figure 4, benzene and cyclohexane resuit as products, each in a purity of 98 per cent.

Example 2 Toluene was extracted from methylcyclohexane at 80 F. in a purity of 98 per cent. For this separation we employed ammonia and ethylene glycol as the solvent. Ethylene glycol was used to the extent of ve per cent in the stripping `zone and thirty-:tive per cent in the enriching zone. to-one.

The solvent-to-oil ratio used was four- Erample 3 Example 4 We have separated methylnaphthalene from paraiins of a similar boiling range by the ammonja solvents. The original concentration of the methylnaphthalene in the hydrocarbon mixture was 30 per cent. This mixture was extracted in a stripping operation at 80 F. with a solvent comprising about 20 per cent monomethylamine and 80 per cent ammonia using a three-to-one solvent-to-oil ratio. The extraction was then continued in an enriching zone. Water was then gradually added to the solvent along the path of solvent flow so that at the extract end of the extraction system the solvent composition was 73 per cent ammonia, 18 per cent monomethylamine and 9 per cent water. These operations yielded methylnaphthalene in the extract of 98 per cent purity. A solvent-to-oil ratio of tWenty-ilve-toone would have been required to obtain this purity and yield of methylnaphthalene if liquid anhydrous ammonia had been used throughout the extraction operation, due to the relatively low solvent power of the ammonia for this feed mixture. Instead of using water as the modifying agent to reduce the solvent power of the ammonia solvent, we could have added ethylene glycol, ethylene diamine, formamide, or lower boiling hydrocarbons such as fractions comprising octane and decane.

Example In the extraction of a straight-run kerosene fraction containing about 30 per cent of aromatics in the molecular weight range of about 130 to 180 we were able to recover aromatics in high purity and yields by countercurrent extraction at ordinary temperatures using ammonia as the solvent. Ammonia enhanced in solvent power by methylamine was used in the stripping zone to recover the aromatics from the feed, while ammonia substantially free of methylamine was used in the enriching section to purify the aromatics. By 1re-extracting these aromatics we were able to obtain a good separation of dicyclic from monocyclic aromatics.

Eample 6 We were also able to separate aromatics containing unsaturated adjuncts from aromatics containing relatively saturated groups. For example, styrene was separated in a high purity from xylenes. This separation was carried out at ordinary temperatures with a solvent comprising ammonia and about per cent water. For feeds containing of the order of 50 per cent styrene a solvent-to-oil ratio of about ve-to-one is satisfactory. Our ammonia solvents afford the additional advantage of a basic medium which greatly stabilizes unsaturated aromatics, especially those containing conjugated systems, as well as other similarly reactive compounds.

Emample 7 Paralnic or naphthenic-type hydrocarbons are desirable modifying agents for reducing the dissolving capacity of ammonia. For example, the solubility of toluene in ammonia is about per centat 15 F. To prepare pure toluene with liquid anhydrous ammonia would require temperatures such as this in the enriching zone. Such refrigeration is expensive. Adding to this system about 1 part of cetane, or 1 to 1.5 parts of decane or decalin resulted in a 15 per cent solubility of toluene at about +50 F. At this temperature toluene alone is, of course, completely miscible with ammonia.

Example 8 Aromatics can be separated from relatively viscous hydrocarbon fractions. For example, aromatics in high concentration are separated from a paralnic oil having about 12 per cent aromatics and a viscosity of about 150 Saybolt seconds at 100 F. when this oil is extracted in a countercurrent extraction apparatus equivalent to about 10 extraction stages with an ammonia solvent containing about 35 to 45 per cent methylamine. With less viscous oils containing more aromatics the proportion of methylamine is less. Also, the addition to the enriching section of a modifying agent to lower the solvent power, such as water, is frequently desirable and affords a very satisfactory means for bringing the aromatics to any desired degree of purity. Liquid anhydrous ammonia is unsuited to extracting oils of the character indicated for it alone possesses too low a solvent power.

The preceding examples, which have been given by way of illustration only, clearly demonstrate the value and utility of our solvent system, based on liquid ammonia and modifying agents as exempliied. Our solvent system possesses outstanding advantages not heretofore available. It is now possible to prepare aromatics in high purity and excellent yields from a variety of mineral oil fractions. As demonstrated it is further possible to separate certain types of aromatics from other aromatic types. In the segregation of one aromatic type from another, ammonia relatively free of modifying solvent is applicable in certain cases. These comprise the reextraction of extracts to purify aromatics, the segregation of mononuclear from dior polynuclear aromatics, and the separation of aromatics having unsaturated groups from aromatics having relatively saturated adjuncts.

Our solvents may be utilized in many different methods of processing in the segregation of aromatics from other components. Most of them are well known to those skilled in the art. For purposes of illustration only, we give the following plant layout which we have found to be a particularly desirable arrangement of apparatus for the use of our solvents. Again for the purpose of illustration only. we have chosen a feed consisting of 25 per cent benzene in paraiiins and naphthenes of a similar boiling point, and a solvent composed of ammonia and water.

The hydrocarbon feed mixture is introduced by means of line I0 into extraction tower II. We have shown the feed being introduced into the top of tower II although an' intermediate feed point could also have been used. By extraction tower II we mean any suitable countercurrent phase contacting device. It may be a series of mixers and settlers, a packed tower, etc. These phase contacting paths are equipped with heating and cooling devices so that the temperature may be controlled at any desirable level or gradients may be employed. For this specific case we prefer that the temperature be controlled at F. The solvent, 5 per cent water in ammonia, is made by mixing water from storage tank I2 with ammonia from storage tank I3 by means of line I4 and pump I5. The mixed solvent is then pumped by means of pump I1 through line I6 into extraction tower II. Here it contacts the down-coming oil phase and dissolves substantially all the benzene together with minor proportions of other components. The extract phase leaves tower I I through line 9. It passes through heat exchanger I8 to point I9 where additional water may be injected if desired. After passing through heater 2| it enters extraction tower Z2 at some point between the -middle and the bottom. Extraction tower 22 is run at a temperature at '80 to 130 F. Water is injected at points 23 along the line of Ysolvent ow to keep the solubility within the desired range. At the top of enriching tower 22, the concentration of water in the solvent will be about 20 per cent. The hydrocarbon phase from this tower is removed at the bottom by line 24, passes through heat exchanger I8, cooler 25 and enters tower II at a point near the top where it joins the feed hydrocarbon. The extract phase at the top of tower 22 consisting of substantially pure benzene dissolved in solvent is removed by line 26 to settler 21.. Water may be injected at point 28 in order to precipitate a hydrocarbon phase. This precipitate settles in settler 21 and is at least partially returned via lines 29 and 30 to the top of extraction tower 22 where it serves as reux.

The solvent phase together with any hydrocarbon phase which has not been returned as reflux is taken from settler 21 by line 3l to evaporator 32. Part of the ammonia is evaporated and is condensed in condenser 34. The condensate is taken by lines 35 and 36 to ammonia storage I3. If desired, some of the hydrocarbon phase which precipitates in the evaporator 32 may be returned as reux to tower 22 by lines 3l and 30. The remainder of the liquid phase is taken by line 38 and pump 39 through heat exchanger lll to distillation column Il I. This column operates at a higher pressure than evaporator 32 so that the remainder of the ammonia which is removed in this column may be removed by line t2 to coil 43 where it condenses and yields the necessary heat to evaporate the ammonia in 32. The condensate from coil 43 is taken by line di and pump e6 to line 36 through which it is returned to ammonia storage I3. Part of the condensed ammonia is returned to column 4I by line l5 to serve as reilux to keep any water or benzene .from distilling over.

Heat supplied to the bottom of column di evaporates the remainder of the ammonia which enters this tower and boils the water in the still to steam strip the benzene. The residue in the still consisting of water and benzene is taken by line il through heat exchanger 60 to cooler d8 and settler t9. The benzene, substantially pure and completely free of ammonia, is removed as nal product at 53. The water is returned via line 5I to storage tank l2 from which it is recycled by pumps I5 and 52 and lines It and 53 to the desired points already mentioned.

The raffinate from the bottom of extraction tercurrent ones illustrated here. Batch, multiple batch, concurrent, or any others familiar to those skilled in the art could be used equally Well. The ammonia solvent may be applied to processes to produce several nal products instead of the usual two. Adjustment of the solvent power to produce these extra portions by precipitation or by further solution is especially applicable. The products mai7 be re-extracted with ammonia solvents of the same or different compositions,

4 or any other devices known to enhance separation, for we are now able to control the solubility tower I l consists of substantially pure naphthenes and paraiilns together with some ammonia. It is removed from the tower by means of line 5ft through heat exchanger 56 to distillation tower 5l. At point 55 some water is introduced for the purpose of stripping the hydrocarbon of all ammonia. Heat supplied to the bottom of column 5l vaporizes all the ammonia and boils the water, steam stripping the hydrocarbon. The ammonia vapors are removed by line 53 to condenser 59. Part of the condensate is returned as reux by line 60 while the remaining is sent to ammonia storage tank I3 via line Si. The

residue in column 5l, consisting of water and hydrocarbon, is removed by line 62 through heat exchanger 56 to cooler 63 and settler 64. The iinal rafiinate, consisting of paraiins and naphthenes substantially free of benzene and completely free of ammonia, is removed at 65. The water may be recycled by line 6l to point 55 or may be returned to storage tank I2.

By operating essentially in the above manner we have been able to make extracts and rainates containing 98 and 2 per cent benzene, respectively, from a feed containing 25 per cent benzene.

If desired, the raffinate from tower ll, consisting of paraiiins and naphthenes, may be taken to another tower where it contacts an ammonia solvent of higher dissolving capacity to separate the naphthenes from the paraiiins. This process is further disclosed in our co-pending application. In this manner, by proper adjustment of the solvent power, the ammonia solvents may be employed to produce several products instead of the usual two in a single process.

While the preceding examples have illustrated the use of the ammonia solvents in extraction towers, their application is in no manner limited to towers alone. Mixers and settlers could be used with equal effectiveness, as well as any other phase contacting devices. These solvents are also applicable to other processes than the counof each of these hydrocarbon types in the ex traction operation so as to make a separation of this sort very practical. The molecular weight range of such a hydrocarbon mixture preferably is within 15 to 30 units in molecular weight, and the narrower this range the sharper the separations become. It is quite easy to prepare any de sired molecular weight range of hydrocarbons by means of distillation. In such a process where the three hydrocarbon types above-mentioned are to be separated, we prefer to segregate the aromatics with unsaturated groups at the end of the enriching section. For a mixture having a molecular weight range of, for example, to 115, an ammonia solvent of reduced dissolving power would be used in the enriching section. At the end of the stripping section the nonaromatic constituents would be withdrawn, having been extracted in this stripping section with an ammonia solvent of somewhat enhanced dissolving power if these non-aromatic constituents predominate in the feed. If the feed is relatively rich, say having the order of 50 per cent total aromatics, the dissolving power of the ammonia solvent used in the stripping section need only be about that of ammonia. At some point between the above-mentioned extract and raiinate ends of this primary extraction system composed of a stripping and an enriching section) the aromatics containing saturated groups will be concentrated. A point is selected in this primary extraction path where these aromatics containing saturated appendages are substantially free of either the non-aromatic constituents of the feed, or else free of the aromatics containing the unsaturated groups. At this point at least a part of one of the phases is withdrawn. This phase is then further extracted in a secondary extraction system (or side stream tower) with an ammonia solvent of the correct dissolving power to free these aromatics containing saturated groups from the other components that were present in the withdrawn side stream. The phase containing the aromatics having saturated adjuncts is withdrawn from this secondary extraction system, and then treated to recover these aromatics from the solvent. The other secondary etxraction phase is then returned to the primary extraction path at a point near the original with drawal point.

A process, such as the one above described. is known as side stream withdrawal. This is a particularly desirable method of processing when using ammonia solvents with multi-component feed mixtures from which more than the usual two products, namely, extract and rafiinate, are desired. Instead of the three hydrocarbon classes above, this same procedure is applicable to the separation of dior polynuclear aromatics from mononuclear aromatics, which in turn are separated from non-aromatic constituents. In this case the polynuclear aromatics are recovered at the end of the enriching section, the nonaromatics from the end of the stripping section, and the mononuclear aromatics are obtained from the side stream tower.

Figure shows one manner by which three or more products may be separated in one integrated process. The hydrocarbon feed is introduced via line 10 into an intermediate point in an extraction path 1|. This may either be a countercurrent column, as shown, or a series of mixers and settlers. Fresh solvent is introduced via line 12 into one end of the extraction path, at which point a final raffinate phase is also withdrawn via line 13. This phase is sent to the usual apparatus for solvent recovery. At the other end of the extraction path, a final extract phase is withdrawn and sent via line 14 to a solvent recovery step 75. Solvent recovery may be by means of distillation, extraction, or any other method well-known to the art. The recovered solvent is withdrawn via line 16 and may be recycled to line 'l2 or first separated into its components by apparatus not shown. The recovered oil from the extract Phase is withdrawn via line 11. Part is withdrawn as product via line 18 and the remainder returned as reux to the main extraction path 1|. Modifying solvents to reduce the solvent power of the ammonia may be introduced at one or more points, 19, along the main extraction path. When the feed consists of three groups of components of different solubility in liquid ammonia, as discussed above, at some point in the extraction path only two of the components will appear in the phases. one of the phases, either extract or raillnate, may be withdrawn and further treated to separate the component of intermediate solubility. A ralnate phase relatively free of components of least solubility may be withdrawn via line 80, at the appropriate point, and extracted in a. contacting device 8|, by fresh solvent of proper solvent power introduced via line 82. The solvent phase from contacting device 8| containing predominantly components of greatest solubility is returned to the main extraction path, 1|, via line 84, to a point near where the raffinate phase was withdrawn. The extacting device 8| containing primarily components of intermediate solubility is withdrawn via line 83 and may then be further treated to remove the solvent. In another case, an extract phase relatively free of components of greatest solubility may be withdrawn via line 85 and sent to a secondary contacting device, 86. If the latter is a countercurrent tower, the withdrawn extract phase enters near the bottom of said tower, 86, while from the top an extract phase is withdrawn via line 8l, sent to a solvent recovery step 88 from which the solvent is removed via line 89 and the oil is removed via line 9|. Part of this latter is withdrawn via line 93 as product containing predominantly components of intermediate solubility while the remainder is re- At this point, part of tracted raffinate phase from the secondary conturned via line 9| as reflux to secondary contactor 86. The raflinate phase from the latter containing predominantly components of least solubility is withdrawn from the bottom via line- 92 and returned to the main extractor path 1| near where the extract phase was originally withdrawn.

Ammonia is the only liquid normally gaseous inorganic solvent known which is capable of being modified with a modifying agent for securing separations herein outlined. It is, furthermore, the only solvent which may be readily separated fro'm the feed oill and which may be also readily separated from the modifying agent. Ammonia is an inorganic solvent which, together with a satisfactory modifying agent as disclosed in the present application, will efficiently and economically separate complex organic substances `such as hydrocarbon oils. As herein modified, it is the only solvent of the character of, for example, sulfur dioxide and sulfuric acid which is wholly satisfactory for separations where these solvents have proven unsatisfactory. It possesses none of the disadvantages of sulfur dioxide or sulfuric acid.

'Ihe following denitions relate to the claims and the preceding specification.

By a predominant proportion of liquid ammonia we mean liquid ammonia together with modifying agent such that the ammonia contributes principally to the solvents selectivity, as illustrated in the preceding examples.

Ammonia solvent means liquid ammonia together with any modifying agent.

By a modifying agent we mean any liquid which when added to the-system will alter the solvent power of the solvent. The modifying agent may or may not be a selective solvent, its determining characteristic being only that it will change the dissolving capacity of the liquid ammonia.

The term zone denotes one or more extraction stages or the equivalent which are properly interconnected, as already demonstrated, wherein continuity of ow and control of operating variables are maintained. By a first zone we mean that portion of the extraction path between which the feed oil enters and the rafinate phase leaves the system. By a second zone we mean an extraction path along the line of solvent ow beyond the point of feed oil introduction. Extracting a feed mixture means extracting this mixture in a first zone. It may also 1nclude the extraction of the more soluble components of the feed' in. a second extraction zone.

Relatively high dissolving capacity means the ammonia solvent dissolves the extractable component or components to a considerable degree, if not completely, and such a solvent is capable of dissolving appreciably the raffinate portions or components. Relatively low dissolving capacity means the ammonia solvent is incompletely miscible with the extractable component or components, and the solubility of such materials in the solvent is usually 20 to 30 per cent or lower, while the raiiinate portions or components are relatively insoluble, i. e., the solubility of such material is of the order of 3 to 10 per cent or less. Reduced dissolving power means that the solvent power is now lower than at some earlier point or stage in the solvent ow path.

By mineral oil we mean mixtures that are predominantly hydrocarbons, such as exist in petroleum or its fractions, or predominantly hydrocarbon mixtures obtained from the processing of carbonaceous materials such as coal, wood. or petroleum or its fractions.

. By aromatics we mean predominantly hydrocarbon compounds containing at least one aromatic nucleus per molecule, i. e., a benzene.,

phenanthrene naphthalene, anthracene, or nucleus. The aromatica may be 'any one of these compounds or derivatives thereof containing one or more of a variety of groups, 'appendages, or linkages which in turn may be either saturated or unsaturated. In general, an aromatic molecule will contain at least one sixmembered carbon ring containing three conjugated double bonds. Aromatics may be characterized by a high density, refractive index, and molecular extinction coemcient in the ultraviolet range. The latter will usually be a maximum in the neighborhood of about 2600 and in general will have a value above 200 for aromatics between a molecular weight of 90 and 200. For certain aromatica in the molecular weight range 25o-dim, vthe molecular extinction co emcient may be as high as l to 100 times this value. Further,` the area under a curve of molecular extinction coemcient versus `wave length in A. between the limits 2800 and 2480 A. will be greater than 430,000 units. Aromatics may be further characterized in the viscous region by values oi density, refractive index, aniline point, and molecular weight which according to the method of Waterman (J. i. P. T., 21, 661,

i935) would be characterized as aromatica.

The term methylamine is used to denote mono, di-, or trimethylamine or mixtures of these.

The present invention is not to be limited by any theory or mode of operation but only in. and by the following claims in which it is desired to claim all novelty insofar as the prior art permits.`

We claim:

l. A process for the segregation of toluene from hydrocarbon mixtures containing it which' comprises extracting said mixtures with liquid ammomia in a stripping and an enriching extraction zone, the temperature of extraction at the point where the solvent enters being controlled between 6W and 140 n". while the temperature of extraetion at the point where the solvent phase leaves the extraction path is controlled between -2`0 d -i-Zii" F.

2. A process lor the segregation oi an aromatic hydrocarbon compound from a drocarbon mixt containing constituents with molecular weights less than about 300 which comprises extracting the leed mixture with a solvent consistof liquid ammonia and a liquid modifying agent selected from substances which reduce the dissolving capacity ofthe ammonia solvent for said aromatic hydrocarbon compound and are soluble in liquid ammonia, under conditions to form ramnate and extract phases, controlling the amount oi hydrocarbon dissolved in the solvent between the limits of 5 to 30 per cent by weicht by addition of said modifying solvent, separat a phase containing aromatic hydrocarbon compound and recovering the solvent and aromatic hydrocarbon compound therefrom.

3. A process as dened by claim 2 in which the modifying agent is water.

a. A process as dened by claim 2 in which the modifying agent is ethylene glycol.

5. A. process as donned by claim 2 in which the modifying agent is a low molecular weight dia.-

t. A process for the segregation oi aromatica from hydrocarbon mixtures containing constituents with molecular weights less than about 300 which comprises extracting the feed mixture with a solvent consisting of liquid ammonia and a minor proportion of methylamine to which is added vin at least a part of the extraction path a solvent modifying agent soluble in liquid ammonia having the ability to reduce the solvent power of the solvent for said aromatics, controlling the amount of hydrocarbon dissolved in the solvent between the limits of 5 to 50 per cent by weight by addition 'of said modifying agent, forming raiilnate and extract phases, separating a phase containing aromatics, and recovering solvent and aromatics therefrom.

7. A process as defined in claim 6 wherein the modifying agent having the ability to reduce the solvent power is water.

8. A process as defined by claim 6 in which the feed mixture comprises hydrocarbon components boiling in the range of about 200 to about 400 F. and the modifying agent having the ability to reduce the solvent power is water.

9. A process as deilned by claim 6 in which atl least a part of the aromatlcs are polynuclear.

10. A pross for the segregation of aromatica of molecular weights less than about 300 from hydrocarbon mixtures containing aromatic components of diii'ering solubility in liquid ammonia, which comprises extracting said mixture with a solvent consisting of liquid ammonia and a modifyina solvent to reduce th'e solvent power of the ammonia for said mixture, controlling the dissolving capacity by addition of said modifying solvent' to limit the amount of hydrocarbon disu solved in the solvent between 5 and 30 per cent by weight and to form an extract phase containing the more soluble aromatics, separating the phases. and recovering solvent and aromatica 40 therefrom.

aromatics, which comprises extracting said mixture with liquid ammonia and a modifying agent to reduce the solvent power oi the ammonia for said feed mixture in a countercurrent treating path comprising a stripping zone and an enriching zone, controlling the solubility of th'e ammonia solvent so that the amount of hydrocarbon dissolved in the solvent is between the limits oi 5 to 30 per cent by weight and so that the most soluble aromatica are segregated at the end of the enriching section in th'e extract phase, and the non-aromatics are segregated at the end oi the stripping section as a railinate phase, further separating at least a part of one of the phases at such an intermediate point in the extraction path that the separated phase contains only the -aromatics of lesser solubility andnon-aromatics together with solvent, and further extracting said separated phases to purify said aromatics of lesser solubility.

l2. A process for the segregation of aromatica of molecular weights less than about 300 from hydrocarbon mixtures containing aromatic compcnents of diderins solubility in liquid ammonia together with non-aromatics, which comprises extracting said mixture with liquid ammonia and a liquid modifying agent to reduce the solvent power of the ammonia for said feed mixture in a countercurrent treating path comprising a stripping zone and an enriching zone, controlling the solubility of the ammonia solvent so that the amount of hydrocarbon dissolved in the solvent is between the limits of 5 to 30 per cent by weight and so that the most soluble aromatica are segregated at the end of the enriching section in the extract phase and the non-aromatica are segregated at the end of the stripping section as a ratlinate ph'ase, further separating at least a part of one of the phases at such an intermediate point in the extraction path that the separated phase contains only the aromatics of lesser solubility and aromatica of greater solubility together with solvent, and further extracting said separating phase to purify the said aromatica of lesser solubility.

13. A process for the segregation of aromatica `from hydrocarbon mixtures containing constituents with molecular weights less than about 300 which comprises extracting the feed mixture in a iirst zone with liquid ammonia and methylamine, separating from the solvent phase a ph'ase containing aromatics, and subjecting said aromatic-containing phase to extraction in a second zone with liquid ammonia.

14. A process for the segregation of aromatics from hydrocarbon mixtures containing constituents with molecular weights less than about 300 which comprises extracting the feed mixture in a iirst extraction zone with' liquid ammonia, adding to the Ysystem a modifying agent to reduce theY solvent power of the ammonia for said aromatics and to control the amount of hydrocarbon dissolved in the solvent between the limits of 5 to 30 per cent by weight and further purifying the aromatics in a second extraction zone.

15. In a process for the segregation of toluene from hydrocarbon mixtures containing it which comprises extracting said mixtures with an ammonia solvent in a stripping and an enriching zone which are maintained at a temperature between 80 and 130 F.. the step of controlling the amount of water in the ammonia so that it is between and 10 per cent at the point of solvent entrance to the extraction system and between 10 and 25 per cent at the point wh'en the solvent phase leaves the extraction system and so that the amount of hydrocarbon dissolved in the solvent phase is between the limits of to 30 per cent byweight:

a,sse,aos

16. A process for the segregation of aromatica with unsaturated side chains from hydrocarbon mixtures containing constituents with molecular weights less than about 300 which comprises extracting the feed mixture with liquid ammonia together with a modifying agent selected from the class of substances which reduce the dissolving capacity of the ammonia for said mixtures under conditions to form ramnate and extract phases, controlling the amount of hydrocarbon dissolved in the extract phase between the limits of 5 to 30 per centby weight by addition of said modifying agent, separating a phase containing aromatics with unsaturated side chains, and recovering solvent and aromatics with unsaturated side chains therefrom.

17. A process as deiined by claim 16 in which the feed mixture comprises components containing from about 8 to about 10 carbon atoms and the modifying agent having the ability to reduce the solvent power is water.

18. The process as defined by claim 16 in which the hydrocarbon mixture predominates in hydrocarbons within the range from. 8 to l0 carbon atoms per molecule. Y

19. A process for the segregation of polynuclear aromatica from hydrocarbons including poly.= and mono-nuclear aromatics and having molecular weights in the range of about to 300, winch comprises extracting said hydrocarbons with a solvent consisting of liquid ammonia and a minor proportion of methylamine to which is added in at least a part of the extraction path a solvent modifying agent having the ability to reduce the solvent power of the said solvent for the aromatics, forming raillnate and extract phases, controlling the amount of hydrocarbon dissolved in the extract phase between the limits of 5 to 30 per cent by weight by addition of said modifying agent. separating a phase containing polynuclear aromatics, and recovering solvent and polynuclear aromatica therefrom.

GEORGE H. CUMMINGS. WILLIAM J. S. MERRELL R. FENSm. 

